Carbon nanotubes have been proposed for use in a number of applications that take advantage of their unique combination of chemical, mechanical, electrical, and thermal properties. Carbon nanotubes display high mechanical strength values (>1 TPa), and a number of structural applications have been proposed, including use as a reinforcing filler in composite materials. Depending on their diameter and helicity, carbon nanotubes can behave as metallic conductors or semiconductors. The electrical conductivity of carbon nanotubes has led to the development of a wide array of devices incorporating carbon nanotubes including, for example, field effect transistors, memory devices and arrays, switches, vias, and other nanoscale electronic devices; batteries; supercapacitors; conductive wires and traces; and the like. The thermal conductivity of carbon nanotubes has led to a number of developments for facilitating heat transfer between surfaces, such as in thermal interface materials.
For heat transfer applications, individual carbon nanotubes can have exceptionally high thermal conductivity values. Along the longitudinal axis of individual carbon nanotubes, thermal conductivity values can range in the thousands of watts/m·K. In contrast, in the transverse direction (i.e., normal to the longitudinal axis), the thermal conductivity is relatively poor. Thus, proper carbon nanotube alignment to achieve optimal thermal conductivity can be desirable. Even in carbon nanotube thin films, alignment can be problematic, and in thicker carbon nanotube layers alignment can be much more difficult.
In many instances, carbon nanotubes have been deposited as a thin film on a substrate or dispersed in a matrix material when utilized in the foregoing applications and others. Thin film forms of carbon nanotubes can include both spin- or spray-coated carbon nanotube films conformally deposited onto a substrate and carbon nanotube mats, fabrics or papers that have been transferred to a desired substrate from another surface. Each of these thin film forms have been used successfully in a number of applications. However, none of these techniques are particularly scalable for bulk applications, particularly for constructing thicker carbon nanotube layers. Although multiple carbon nanotube mats can be placed upon one another to form thicker carbon nanotube layers, there can be sub-optimal nanotube-to-nanotube contact between the layered mats, thereby reducing the overall mechanical strength and electrical/thermal conductivity. Carbon nanotubes can also be directly grown onto a number of substrates (e.g., by chemical vapor deposition), but scalability can again be problematic in a number of instances and there is only limited opportunity to control the carbon nanotube morphology on the substrate.
In view of the foregoing, techniques that allow thicker carbon nanotube layers to be formed in a desired morphology and processed into three-dimensional articles would represent a significant advance in the art. The present disclosure satisfies the foregoing needs and provides related advantages as well.